Merge remote-tracking branch 'remotes/thuth-gitlab/tags/pull-request-2021-08-25' into staging

* Various updates for the documentation

# gpg: Signature made Wed 25 Aug 2021 11:27:27 BST
# gpg:                using RSA key 27B88847EEE0250118F3EAB92ED9D774FE702DB5
# gpg:                issuer "thuth@redhat.com"
# gpg: Good signature from "Thomas Huth <th.huth@gmx.de>" [full]
# gpg:                 aka "Thomas Huth <thuth@redhat.com>" [full]
# gpg:                 aka "Thomas Huth <huth@tuxfamily.org>" [full]
# gpg:                 aka "Thomas Huth <th.huth@posteo.de>" [unknown]
# Primary key fingerprint: 27B8 8847 EEE0 2501 18F3  EAB9 2ED9 D774 FE70 2DB5

* remotes/thuth-gitlab/tags/pull-request-2021-08-25:
  docs: make sphinx-build be quiet by default
  docs: split the CI docs into two files
  docs/about/removed-features: Move some CLI options to the right location
  docs/about: Add the missing release record in the subject
  docs/about: Unify the subject format
  docs/about: Remove the duplicated doc

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>